This invention relates generally to the detection of alpha radiation and relates, more particularly, to instruments used in the detection of alpha radiation.
Conventional alpha scintillation survey instruments commonly include an optically-transparent light pipe which is optically coupled to the front of a photomultiplier tube. Disposed across the light pipe opposite the photomultiplier tube is a thin layer of phosphor, such as silver-activated zinc sulfide. During use of such an instrument, alpha particles interact with the phosphor layer to create light photons which, in turn, are guided by the light pipe onto the photomultiplier tube. In order to protect the photomultiplier tube from saturation by ambient visible light, the instrument is commonly housed in a metal casing and covered with a thin, opaque radiation entrance window.
The entrance window is relatively thin to permit the passage of alpha particles and to avoid any significant reduction of kinetic energy possessed by the particles as they pass through the window. Entrance windows of conventional alpha scintillation instruments commonly are provided by a layer of aluminized Mylar.RTM. possessing a thickness of about 6.35 micrometers (i.e., about 0.25 mil). Mylar.RTM. material possessing such a thickness is known to provide a satisfactory opaque shield against ambient light and is thin enough for most alpha particles to penetrate. However, such a window is relatively fragile and is easily punctured, torn or scratched. In order to render a conventional survey instrument more durable for use in field environments, the fragile entrance window may be replaced with a meshed Mylar.RTM. window screen or a micromachined silicon wafer may be incorporated Within the instrument to obviate the fragile entrance window. However, neither of the instruments which result from the aforementioned use of the meshed window screen or micromachined silicon wafer have been found to be both highly efficient and suitably rugged. It would be desirable to provide an instrument for the detection of alpha radiation which combines both high efficiency and ruggedness.
Accordingly, it is an object of the present invention to provide a new and improved scintillator assembly for use in an alpha radiation detector which promotes high efficiency during operation of the instrument and is sufficiently rugged for use in field environments and a method of making the assembly.